1. Field of the Invention
The present invention relates to an image-processing integrated circuit device for carrying out the two-dimensional FIR (Finite Impulse Response) digital filtering processing of image data.
2. Description of the Prior Art
Heretofore, two types of image-processing integrated circuit devices have been used for carrying out the two-dimensional FIR digital filtering processing of image data, one being a device using a plurality of one-dimensional digital filter LSIs (Large-Scale Integrated Circuits) in combination, the other being a device using a two-dimensional digital filter LSI.
First Prior Art System
Referring to FIG. 7, there is shown a first prior art example using a plurality of one-dimensional digital filter LSIs in combination and having a window size of 5.times.5. In FIG. 7, there are provided an input terminal 1, line delay buffers 2-1 through 2-4, one-dimensional digital filter LSIs 3-1 through 3--3, an interface 4, a host CPU (Central Processing Unit) 5, and an output terminal 6.
FIG. 4 shows image data in a 5.times.5 window. Image data in the 5.times.5 window are supplied successively through the input terminal 1. For example, image data in a row M.sub.1 as shown in FIG. 4 are supplied successively in the order of d.sub.15, d.sub.14, d.sub.13, d.sub.12 and d.sub.11.
When one row of the image data constituting the window are supplied, the data are delayed by the line delay buffer 2-1 for a period required for reading one line in a screen. Thereafter, whenever one row of the image data constituting the window are supplied, the row of image data are delayed in the same manner as described above. Such delay makes it possible to feed all the image data into the one-dimensional digital filter LSIs 3-1 to 3--3 simultaneously and timely when the last fifth row of the image data are supplied.
Filtering processing is carried out by multiplying the image data by coefficient data and by adding the results of the multiplications.
FIG. 5 is a view showing coefficient data determined corresponding to the image data in the 5.times.5 window. For example, .omega..sub.11 represents a coefficient data by which the image data d.sub.11 is multiplied, and .omega..sub.15 represents a coefficient data by which the image data d.sub.15 is multiplied.
The values of the coefficient data are given corresponding to the respective image data in the window. However, the coefficient data of the same value may be given for image data in different positions within the window. For example, the same value may be given for image data in symmetrical positions within the window. Various methods can be used for designating such symmetrical positions. As one method, the same value may be given for image data being vertically, horizontally and obliquely symmetrical with respect to the center (the position of d.sub.33 in FIG. 4) of the window.
FIG. 6 is a view showing an example of symmetry in coefficient data in the 5.times.5 window. In this example, the positions of the same alphabet designate symmetrical positions. Accordingly, the coefficient data .omega..sub.11, .omega..sub.15, .omega..sub.51 and .omega..sub.55 in the symmetrical positions a have the same value.
Therefore, in FIG. 7, the image data in the rows M.sub.1 and M.sub.5 having a symmetrical relation are fed to the one-dimensional digital filter LSI 3-1; the image data in the rows M.sub.2 and M.sub.4 are fed to the one-dimensional digital filter LSI 3-2; and the image data in the remaining row M.sub.3 are fed to the one-dimensional digital filter LSI 3--3.
In each of the one-dimensional digital filter LSIs, the image data are multiplied by the coefficient data corresponding to the aforementioned symmetrical positions and then the results of multiplications are added to each other. Lastly, the sum of the results of addition in the one-dimensional digital filter LSIs is obtained as a filter output from the output terminal 6.
The operation of the one-dimensional digital filter LSIs 3-1 to 3--3 is controlled by the host CPU 5 through the interface 4.
Second Prior Art System
Referring to FIG. 8, there is shown a second prior art example using a two-dimensional digital filter LSI and having a window size of 5.times.5.
Items in FIG. 8 corresponding to those in FIG. 7 are referenced correspondingly. In FIG. 8, the reference numeral 7 designates a coefficient RAM (Random Access Memory), 8 a two-dimensional digital filter LSI, 9 a control circuit, and 10 a multiplexer. The coefficient RAM 7 is provided for storing coefficient data therein by which image data are multiplied.
The two-dimensional digital filter LSI 8 shown in FIG. 8 can carry out two-dimensional digital filtering processing by itself, but cannot process all the data in the window simultaneously. In short, the LSI 8 cannot but process all data rows which are constituent members of the window. Accordingly, the data must be fed to the LSI 8 through the multiplexer 10, row by row.
The control circuit 9 is provided for controlling operation of the multiplexer 10 and for controlling the address of the coefficient RAM 7.
Problems in the prior art are as follows.
Problems in the first prior art system are: (a) a large number of parts are required; and (b) it is impossible to change filtering characteristics in a real-time operation in the middle of filtering processing to obtain higher picture quality.
It is apparent from FIG. 7 that parts increase in number because a plurality of one-dimensional digital filter LSIs are required for carrying out two-dimensional digital filtering processing.
The reason why the filtering characteristic cannot be changed in a real-time operation is as follows.
In each of the one-dimensional digital filter LSIs shown in FIG. 7, multiplication can be carried out by using a multiplier or by a table look-up method in which the results of image data multiplied by coefficient data are stored in the form of a table in a RAM in advance so that the results can be respectively read when the image data are given as addresses.
In the case where such a table look-up method is employed, the filtering characteristic is determined by values in the table. Accordingly, the values in the table must be rewritten if a different filtering characteristic is required. It is, however, impossible that the rewriting be carried out in a real-time operation in the middle of filtering processing according to the requirement. In short, it is impossible to change the filtering characteristic in a real-time operation.
Problems in the second prior art example are in that (a) a large number of parts are required; and (b) the processing speed is slow.
It is apparent from FIG. 8 that parts increase in number because the coefficient RAM 7, the control circuit 9, the multiplexer 10 and the like, as well as the two-dimensional digital filter LSI 8, are required.
The reason why the processing speed is slow is that the two-dimensional digital filter LSI 8 cannot process all the rows of data in the window simultaneously and must process the data given by the multiplexer, row by row.